That's the answer I give when people ask me how I chose infectious diseases as my subspecialty. Detective work in infectious disease involves reasoning from the perceptual level, according to the laws of logic, to arrive at a diagnosis and formulate a treatment plan. This method, which has both deductive and inductive aspects, is not exclusively applicable to medicine, but all of life. One realm, however, where it is employed in a striking manner is in forensic science and the practitioner par excellence is the fictional Sherlock Holmes who, fittingly, was the creation of the physician Sir Arthur Conan Doyle.

Tuberculosis can scarcely be mentioned without thinking of Robert Koch, the Nobel Prize-winning physician. Koch definitively proved that the dread disease was caused by an invading pathogen, Mycobacterium tuberculosis. Such a discovery provided further evidence of the veracity of the germ theory of disease, which was catapulted from fringe hypothesis status by Louis Pasteur. Koch's contributions to the study of tuberculosis, anthrax, cholera, and other infectious diseases--in my view and in Goetz's--pale before the enormous feat he performed in developing and articulating his eponymous postulates. The postulates form the basis for proving a pathogen is the cause of a disease in question. This achievement, as Goetz recognizes, cannot be understated.

The other strand of the story told is that of Sir Arthur Conan Doyle, a physician in practice who longed to be a writer. Goetz writes of how Doyle employed his medical worldview, which consisted of meticulous observation coupled with deductive reasoning, to create the character of Sherlock Holmes, who first appeared in two early novels. However, Holmes ascended as a celebrity in his own right after a fascinating incident: Koch's mistaken claim regarding tuberculin. What Koch claimed was that tuberculin, a glycerin extract of M.tuberculosis now in common use in tuberculosis skin testing, was a remedy for tuberculosis. Doyle, dispatched to Germany as physician correspondent for an English paper, was unconvinced of the data behind this claim and his subsequent article helped to publicize the errors behind what came to be a scandal over tuberculin. Doyle soon fully committed to writing and left medicine; Sherlock Holmes soared to the point that he even eclipsed his creator.

The book also contains many historical gems, provides a thorough treatment of how the germ theory increasingly gained acceptance one mind at a time, and concretizes how medicine (and detective fiction) was revolutionized.